This invention relates to a novel construction of inflatable bag for use in a mine support, to a mine support incorporating the bag and also to a method of installing the support.
Props for supporting the roof have been used in mines for many years. More recently mine supports have been developed which comprise in addition to a prop in the form of an elongate timber member, a headboard (to be placed at the upper end of the prop) on which an inflatable bag can be supported. During installation the bag is positioned in a deflated condition on the headboard, between the upper end of the prop and the mine roof. The bag is then inflated to a substantial pressure with a settable grout with the result that a substantial force is applied axially to the prop. Such mine supports have been described in U.S. Pat. Nos. 5,288,178; 5,149,228; and 5,427,476. However these supports are time-consuming to install because in many cases the props need to be sawn on site to obtain the correct length.
U.S. Pat. No. 4,277,204 describes a mining support which comprises single section or telescoping multi-section tubes made of a light sheet material containing a fabric bag which is filled with a hardenable slurry which, on hardening, forms a column to support the overburden. The casing has no supporting function and may be removed or left in place.
Alternatively, there have been proposals to employ as the prop a steel tube into which is pumped a settable load bearing material such as grout. For example, South African Patent No 90/1210 describes a mine support made of a steel tube into which a filling material such as grout is pumped. To accommodate variations in the height of the mine roof above the floor the tube is able to telescope within another tube having a ductility of at least 18%. The filling material forms a column within the tubes. The ends of the tubes are closed by a flexible sheet material which may be glued into position. This arrangement is not suitable nor intended to be pressurised. In an alternative embodiment this patent describes the provision of a separate bag which is placed in position at the top of the assembly after the tubes have been filled. The bag is then filled under pressure. The flexible character of the bag is said to result in it following the contours of the hanging wall.
Because the bag is provided as a separate part, it is necessary to discontinue the filling operation after the tubes have been filled, place the bag in position and then fill the bag under pressure whilst maintaining it in the correct position.
Patent Application No. WO 97/47859 describes a mine support which overcomes this problem in which the support comprises a tube having attached to its upper end a diaphragm which is capable of being inflated and stressed against the roof of the mine and which is sufficiently flexible to follow the surface irregularities in the roof of the mine. The support can be filled with load bearing material in a continuous operation.
Problem to be Solved by the Invention
However it has been found that there is some risk of damage during transit to the diaphragm of the mine support described in Patent Application No WO 97/47859. In addition the preferred embodiment of the mine support which has two tubes, one telescoping inside the other, requires a seal between the telescoping tubes.
The present invention provides a solution to this problem by the provision of a flexible bag for use in the tube, to which bag a load bearing material is supplied to inflate the bag against the roof of the mine.
According to the present invention there is provided a support for use in mines and other underground workings said support being inflatable by superatmospheric pressure and comprising:
(i) a tube to be installed where it is desired to provide support, the tube having
(ii) a flexible bag located within the tube, the bag having an inlet for the admission of a pumpable load bearing material and an outlet for releasing air from the bag, the bag being made of a material that permits it to be inflated and stressed against the roof of the mine by the pumpable load bearing material under a superatmospheric pressure and of sufficient flexibility to follow the surface irregularities in the roof of the mine.
Advantageous Effect of the Invention
The advantage of the present invention is that the risk of damage during transit is greatly reduced and there is no need to provide a separate seal between the telescoping tubes.